Détermination des débits dans les rivières herbeuses

Ingénieur des Ponts et Chaussées à la première Circonscription électrique.

Résumé

The author relates the difficulties he has experienced in attempting to determine discharge in streams in the Seine river basin and northern France due to thick growths of weeds in the streams in summer ; due to the shallow slope of these streams, fine silt settles out on which a thick growth of weeds develops, causing an appreciable difference in water levels (sometimes of over 20 cm) between winter and summer. This is particularly troublesome as many of these streams are broad and give an unsensitive low-water rating curve. As it is seldom practicable to install artificial discharge measurement equipment (e.g. weirs, etc.), emergency solutions have to be resorted to, which frequently provide sufficiently accurate results. The author mentions the following : (i) Determination of a 'calibration loss' curve every summer from several measurements in situ. (ii) Correlation by single measurements with neighbouring gauging stations subject to little or no disturbance. (iii) Extrapolation of discharge duration curves to the low flow range. Quantitative data on the phenomenon observed at two different gauging stations are given in an Appendix.